Load impact controller for a speed regulator system

ABSTRACT

An impact load controller (28) compensates for the speed drop of a drive motor (12), which speed drop is caused by a load disturbance applied to the drive motor (12). A change in the dynamics of a speed controller (30, 34) in a speed regulator system for a stand in a tandem rolling mill is initiated by detecting a speed error (WE) which is greater than a predetermined speed error value and is removed after the speed error has been reduced to a predetermined value. The controller (28) is a pure rate controller whose input is converted into a rate change in speed error, which is multiplied by a gain factor. The resultant gain value product is initially increased by a predetermined factor to provide a high input signal to the (PI) speed controller (34) of a multi-loop speed regulator system for the drive motor (12), and to precharge a low pass filter. Thereafter, the output of the impact load controller (28) is a function of the time constant of the low pass filter; whereby the product gain consisting of the rate of change in speed error decays exponentially. The load impact controller (28) can be either a microprocessor type of control arrangement or an analog type of control arrangement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a speed regulator system for a d.c. motor, andmore specifically to an impact load controller for use with a speedcontroller of such a system.

2. Description of the Prior Art

In the threading stage of a hot or cold tandem rolling mill for rollingmaterial, such as a steel strip, the strip passes through several standsof the mill. The entry of the strip into the roll bite of the standcauses an impact load torque to be applied to the drive motors of thework rolls which are pulling the strip through the roll bite. When thisload is applied to the speed regulator system, the drive speed suddenlydrops. Any drop in drive speed of the stand which is being threaded willcause the strip to gather or buckle between the stand being threaded andthe previous stand from which the strip has exited. The increase instrip storage will result in reduction or loss in the tension in thestrip between the two stands in which the strip is being threaded. Thisloss in interstand tension in the strip is a serious operational problemfor the mill, forcing the mill operator to manually operate the controlsto change the drive speed of the stand or stands for the threadingoperation.

This manual operation of the controls sometimes results in an excessiveincrease in the drive speed and thus, an excessive removal of stripstorage between the stands, resulting in strip breakage.

It is not only important that the drive speed of the stand in which thestrip is being threaded speed recover as fast as possible, but also toovershoot a safe amount to quickly remove the strip storage between thestands caused by the speed drop due to the load impact to the drivemotor without causing breakage to the strip.

Previous attempts may have been made to compensate for this impact loaddisturbance applied to a speed regulator drive system of a millresulting in a speed drop of the drive motor. However, none of thesesystems have achieved this compensation in the same manner and with thesame efficiency provided by the present invention.

The present invention uses an impact load controller which operates onthe rate of change in speed error to first cause the stand speed toovershoot within safe limits and then to quickly bring this overshootspeed down to the threading speed or reference speed setting of themill.

SUMMARY OF THE INVENTION

This invention employs an impact load controller used with a (PI) speedcontroller in a speed regulator system for a drive motor and is used forcompensating for the speed drop caused by a load disturbance applied tothe motor.

This is accomplished by providing an impact load controller which has ameans and a method for determining the difference between the presentspeed error and the previous speed error, which speed errors arecontinually being updated. This difference in the speed error values ismultiplied by "Goose Gain" factor to produce a gain value. This gainvalue product is initially increased by a rate factor, which signal isinitially applied to a low pass filter for precharging the low passfilter and to a summer device for operating the (PI) speed controllerused in the speed regulator system. After a few milliseconds, the gainvalue product of the impact load controller is changed due, in part, tothe updated values of the present speed error and the previous speederror. The new gain value product passes directly to the low passfilter. The output from the low pass filter is combined with the speederror signal and optionally with an output of a (PI)² speed controllerwhich also operates on the speed error signal for an output signal froma summer device. This output from the summer device is produced for adesired time period, for example, two (2) seconds after the strip hasentered the roll bite, to operate the (PI) speed controller. At thistime, the impact load controller and the (PI)² speed controller areturned off, whereby the (PI) speed controller resumes its normaloperation by operating solely on the speed error signal.

This control arrangement for the impact load controller of the inventionmay be a digital based microprocessor or an analog type of controlsystem. As applied to a speed controller for a rolling mill, forexample, the impact load controller operates on a "strip in stand" logicsignal, and is part of the main logic control for the mill. Theconditions which must be meet for operation of the logic system differfor a cold mill and a hot mill.

It is, therefore, a broad object of the present invention to provide ameans and method for quickly and efficiently compensating for speed dropof a drive motor caused by an impact load applied to the motor.

It is a further object of the present invention to provide a means andmethod for automatically compensating for speed drop of a drive motor ofa mill stand caused by an impact load when a workpiece initially entersthe roll bite of a stand during the threading phase of the mill.

It is still a further object of the present invention to provide a meansand method for compensating for speed drop by rapidly recovering thespeed with sufficient overshoot which does not result in breakage of theworkpiece.

A still further object of the present invention is to provide an impactload controller which may be a microprocessor or an analog type controloptionally used with a (PI)² speed controller, and which impact loadcontroller is operated for only a few seconds after the workpiece is inthe mill stand.

A still further object of the present invention is to provide a meansand method for changing the dynamics of a (PI) speed controller toreduce the effect of an impact load disturbance on the response of aspeed regulator system.

A still further object of the present invention is to provide an impactload controller whose output is a function of the rate of change in thespeed error, whereby this rate of change in speed error is a directfunction of the magnitude of the impact load torque disturbance appliedto the drive motor, that is, the greater the load, the greater theoutput signal of the impact load controller.

It is a still further object of the present invention to provide a meansand method of producing a supplemental signal which is a function of therate of change in speed error and which is combined with an error signaland, optionally, with an output signal of a (PI)² speed controller tocontrol a (PI) speed controller for regulation of a drive motor.

It is a further object of the present invention to provide an impactload controller which is self-adapting to varying impact loads, therebyproviding optimum reduction in the speed error for a drive motor.

These and other objects of the present invention will be more fullyunderstood from the following description of the invention, on referenceto the illustrations appended thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a multiloop speed regulator system for adrive motor incorporating the present invention;

FIG. 2 is a schematic showing of two stands of a tandem rolling millillustrating the material storage problem which is solved by the presentinvention;

FIG. 3 is a detailed block diagram showing the invention and some of thecomponents of FIG. 1;

FIG. 4 illustrates the derivation of the rate dynamics for the transferfunction of the impact load controller of the invention;

FIG. 5 shows a software diagram of the impact load controller of thepresent invention;

FIG. 6 shows a more detailed block diagram of the impact load controllerof the present invention;

FIGS. 7A and 7B show a logic diagram for operating the presentinvention;

FIGS. 8A, 8B, 9A, 9B, 10A, 10B, 11A, and 11B are flow charts for theimpact load controller of the invention;

FIG. 12 shows curves (a) and (b) for a proportional integrator squared(PI)² speed controller with the (PI) speed controller and without theimpact load controller of the invention; curves (c) and (d) for aproportional integrator squared (PI)² speed controller with the (PI)speed controller and with the impact load controller of the invention;

FIG. 13, curves (a) and (b) are curves for a proportional integrator(PI) speed controller without the (PI)² speed controller and the impactload controller of the invention; curves (c) and (d) are curves for aproportional integrator (PI) speed controller without the (PI)² speedcontroller and with the impact load controller of the invention;

FIG. 14 curves (a)-(c) are curves for a proportional integrator squared(PI)² speed controller similar to that of FIGS. 12c and 12d andincluding an output signal for the impact load controller of theinvention;

FIGS. 15A and 15B are schematic diagrams of an analog form of the impactload controller of the invention; and

FIG. 16 is a schematic diagram of the speed error detectors and thetransfer functions for the analog control of FIGS. 15A and 15B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a simple schematic of a speed regulator system 10 foroperating a direct current drive motor 12 connected to be energized by athyristor armature supply (TAS) 14 in response to an armature voltagereference signal from an armature current controller 16, which may have(PI) characteristics. An armature current sensor 18 provides an actualcurrent negative feedback signal to a summer device 20. Summer device 20generates an armature current error signal which is the differencebetween an armature reference between an armature reference current Ia*and the actual current Ia.

The speed of drive motor 12 is detected by a digital tachometer 22 whoseoutput is converted into a desired voltage by drive speed sensor 24. Theoutput from sensor 24 is a feedback signal W, which is negative, and isfed to a summer device 26, which also receives a desired motor speedreference W*, which is positive. The output from summer device 26 is aspeed error signal WE.

During the normal operation of the system for the drive system of FIG.1, the speed error WE is used to control the normal speed controller forthe system. For the invention, this speed error signal WE is used assimultaneous input to impact load controller 28, (PI)² integrator 30,and summer device 32. These three inputs to summer device 32 arepositive. The invention involves impact load controller 28.

For an operation of a preferred embodiment of the invention, the speederror WE signal is directed along line L₁, to summer device 32, andalong lines L₂ and L₃ to impact load controller 28 and (PI)² speedcontroller, respectively. If (PI)² speed controller is not used, thenthe WE signal is directed only along lines L₁ and L₂. When the inventionis not operating, i.e. the impact load controller 28 is turned off, thenpreferably (PI)² speed controller 30 is also turned off, and the WEsignal only goes to summer device 32 for operation of (PI) speedcontroller 34. The (PI) speed controller 34 is normally used for theoperation of drive motor 12.

An example of a speed controller 30 having (PI)² characteristics can befound in U.S. Pat. No. 3,775,653 which issued on Nov. 27, 1973 to thesame inventor as the present invention. In this U.S. Pat. No. 3,775,653a speed controller with (PI) characteristics is also discussed. In viewof this, both speed controllers 30 and 34 in the invention arewell-known in the art, and therefore, little or no further discussionwith regard to these components is necessary for a completeunderstanding of the invention.

Also, as is known in the art, the block diagram of FIG. 1 is a multiloopspeed regulator system with components 14, 16, 18, and 20 comprisinginner current loop 36, and with components 24, 26, 28, 30, 32, and 34comprising outer speed control loop 38. FIG. 1 shows a simplifiedversion for the current loop, however, it is to be noted that the systemin U.S. Pat. No. 3,950,684 which issued on Apr. 13, 1976 to the presentinventor can be used. This system includes a current reference rampfunction generator. Also, the system of U.S. Pat. No. 3,983,464 issuingon Sep. 28, 1976 can be used with obvious modifications to include theinvention.

FIG. 2 shows the speed regulator system 10 of FIG. 1 which drives d.c.drive motors 12 which, in turn, drive the work rolls in a downstandstand 40 of a tandem mill. This FIG. 2 illustrates the problem occurringin a strip S when the strip leaves stand 42 and enters the roll bite ofstand 40. When an impact load is applied to stand 40, the speed of thework rolls in stand 40 is decreased, and the strip gathers betweenstands 40 and 42. The dashed lines indicate that the strip is beingstored between stands 40 and 42, and the solid line represents a tautstrip between the two stands 40 and 42.

FIGS. 3, 5, and 6 show in detail the impact load controller 28 of theinvention, and FIG. 4 shows the derivation of the rate dynamics for theimpact load controller 28.

Before further discussing the description and operation of the presentinvention, it is to be noted that the armature current reference Ia* inFIGS. 1 and 3 is generated during the normal operation of the mill by(PI) speed controller 34. The transfer function of the PI speedcontroller shown in FIG. 3 is

    (1+T.sub.1 S)/T.sub.x S

where

S=Laplace operator (1/sec.)

T₁ =current controller lead time constant (sec.)

T_(x) =current controller integrator time constant (sec.).

The output of PI controller 34 is electrically coupled to thyristorarmature supply (TAS) 14 (FIG. 1) which has associated therewith thefollowing transfer function:

    K.sub.v e.sup.T.sbsp.d.sup.S

where

K_(v) =TAS static gain, and

T_(d) =TAS transport time delay (sec.)

The transfer function for the (PI)² speed controller 30 is given in U.S.Pat. No. 3,775,653 discussed hereinbefore, and represented is FIG. 3 by1/T₂ S, where T₂ is a time element and S is the Laplace operator. Thesymbols to the right of (PI) speed controller 34 in FIG. 34 in FIG. 3represent limits for the field flux φ_(f) of motor 12 and for thearmature reference current I_(a) *, and the transfer function 1÷φ_(f)for motor 12. These components are further explained in U.S. Pat. No.3,950,684 cited hereinbefore.

As mentioned hereinbefore, the operation, transfer functions, etc. ofthe components in FIGS. 1-6, with the exception of impact loadcontroller 28, are conventional and need not be further discussed.Therefore, only impact load controller 28 of the invention will bediscussed further with reference to FIGS. 3-16. It is to be noted thatthe impact load controller 28 of the invention can be either of thedigital type microprocessor arrangement with the flow charts for aprogram being shown in FIGS. 8A-11B, or of the analog type arrangementshown in FIGS. 15A-16.

Particularly referring to FIG. 4, there is shown symbolically thederivation for the transfer function of load impact controller 28:##EQU1## where

X=Input

Y=Output ##EQU2##

S=Laplace operator (1/sec.).

The Laplace operator, S, (1/sec.) is set equal to ##EQU3## where Z⁻¹ isa memory circuit equal to e^(-T) d^(S), and T_(d) is an updated time inmilliseconds for the digital controller of the microprocessor used inthe invention.

If ##EQU4## then the output for the impact load controller 28 of theinvention is: ##EQU5## where in FIG. 5, the flow charts of FIGS. 8A-11B,K_(g) /T_(d) is indicated as being (GOOSE GAIN) and 1-Z⁻¹ is indicatedas being [WEG-WEGZ]. WEG represents the present speed error, and WEGZrepresents the previous speed error in the memory circuit of the impactload controller 28.

As shown in the bottom portion of FIG. 4, the speed error WE, which isthe output of summer device 26 shown in FIGS. 1 and 3 represents theinput to impact load controller 28, and the altered output isrepresented by WIG which is the input signal to summer device 32.

FIGS. 5 and 6 show in greater detail the impact load controller 28 ofthe invention.

Referring now to FIGS. 5 and 6, there is shown unit 44, multiplier 46,summer device 48, low pass filter 50, and summer device 52. FIG. 6additionally shows a tuning device 54 for unit 44, and a tuning device56 for filter 50.

As indicated in FIG. 6, tuning device 54 can change or fine tune thegoose gain value of unit 44 in a range of absolute values from zero to15, and tuning device 56 can adjust or fine tune the goose filter timeconstant of low pass filter 50 in a range from zero to 200 milliseconds.These tuning devices 54 and 56 are equivalent to a potentiometer in ananalog electrical type control arrangement for load impact controller28, or can be incorporated into the program in a digital basedmicroprocessor control arrangement for load impact controller 28.

As shown in FIG. 6, low pass filter 50 is a first order filter andoperates on the following transfer function: ##EQU6## where

TC=time constant for the filter, and

S=Laplace operator (1/sec.).

The time constant is set by the values of the resistor and capacitorelements for the electronic equivalent for filter 50. In FIGS. 5 and 6,unit 44 contains a gain factor which is represented by (GOOSE GAIN) anda rate of the change in the speed error which is represented by[WEG-WEGZ], where, as stated hereinbefore, WEG represents a presentspeed error value and WEGZ represents a previous speed error value. Thegain factor (GOOSE GAIN) is a multiplier for the difference between thepresent speed error value and the previous speed error value. The valuesin parenthesis and in the brackets of unit 44 contain variables, whichchange the output of unit 44, more about which will be more fullyappreciated hereinafter.

With regard to the multiplier 46 of FIGS. 5 and 6, the output from unit44 is increased an amount which is indicated in block 46 as being "2^(RATE) SHIFT ". This value is a representation for a binary addresslocation, where it is conventionally known that if the location isshifted two places to the left, the input is multiplied by the integerraised to a power, and if the location is shifted to the right in theregister, the input is divided by the integer raised to a power. In thisparticular instance, the base integer is always the numeral "2" raisedto a power ranging from 0 to 5. From the above, it can be appreciatedthat the tuning parameters for the impact load controller 28 are the"GOOSE GAIN" of unit 44, the Goose Filter Time Constant of filter 50,and the multiplier of element 46. Once these parameters are set for aparticular operation, they remain fixed throughout that operation.

Also shown in FIGS. 5 and 6 are logical switches indicated as beingGFLAG and FIRST GOOSE. The GFLAG logical switches are associated withunit 44 and filter 50 for their operation and deactivation, and theGOOSE FILTER switches, FG1, FG2, and FG3, are associated with the lowpass filter 50, for its initial precharging, and for its output beingeither connected or interrupted with respect to summer device 52, moreabout which is discussed hereinafter.

The impact load controller 28 of the invention operates on a logicsystem which is part of the main logic system for the mill. An examplefor such a logic diagram is shown in FIGS. 7A and 7B. When the logicsignal "GFLAG" is True, the Goose Control of the load impact controller28 is energized. A speed error WE or WEG input enters unit 44, whichoperates on the transfer function of FIG. 4. When the Goose Control isfirst energized, the FIRST GOOSE Logic Command is True, and the initialoutput from unit 44 goes into multiplier 46, where its value isincreased by a factor of 2^(RATE) SHIFT =4, where "RATE SHIFT",preferably, is equal to 2. This initially gives a high input signal toPI controller 34. At the same time, i.e. when the output from multiplier46 is directed to summing device 52 of FIG. 5, this output from unit 46is also directed to low pass filter 50 to precharge filter 50, with nooutput from filter 50 being directed to summing device 52.

After this initial precharge of impact load controller 28, the FIRSTGOOSE logic signal is set to "False", which opens the logic switch FG 2and closes the FIRST GOOSE logic switch FG1 shown in FIGS. 5 and 6. Theoutput from the product gain unit 44 is reduced since multiplier 46 isnow bypassed, with the output from unit 44 directed to summer device 48,and then to the low pass filter 50. The FIRST GOOSE switch FG3associated with filter 50 is now closed allowing its output to bedirected to summer device 52 for an output designated as WIG as shown inFIGS. 5 and 6.

Preferably, the (PI)² speed controller (FIG. 1) will operate inconjunction with the impact load controller 28 to receive the errorsignal WE and to produce an output for a total of three inputs to thesummer device 32 of FIG. 3, as explained hereinbefore. When impact loadcontroller 28 is not operating, the (PI)² speed controller 30 is turnedoff, so that the only input to summer device 32 is the speed error WEfrom summer device 26, shown particularly in FIG. 3. The impact loadcontroller 28 is a pure rate controller in that a derivative or rate ofchange in speed error is used to change the dynamics of the multi-loopspeed regulator system 10 of FIG. 1. The dynamics of the impact loadcontroller 28 is a pure rate cascaded through the low pass filter 50. Atthe initial turn "on" of the impact load controller 28, the controller28 is a pure rate controller with a high gain. The gain factor 2^(RATE)SHIFT in the multiplier 46 can be increased or decreased by increasingor decreasing the integer value of "RATE SHIFT". The gain (GOOSE GAIN)for impact load controller 28 and the time constant "GOOSE FILTER TC"for the low pass filter 50 can be adjusted by a tuning device 54, 56respectively. These adjustments, as well as the adjustment to multiplier46, are only done in the mill set-up and not during the operation of theinvention or the mill.

Preferably, the impact load controller 28 and (PI)² speed controller 30are only used in the threading phase of the mill when the stripinitially enters the roll bite of a stand. Also, preferably, these twocomponents 28 and 30 remain in operation during this threading phase foronly two (2) seconds after the strip enters the roll bite. Both impactload controller 28 and (PI)² speed controller 30 can be reset to zero inpreparation for the next threading operation of the mill.

The impact load controller 28 is energized when one or more conditionsare satisfied. These conditions appear in the logic diagram of FIGS.7A-7B, which also shows a speed error curve and a GFLAG=TRUE curveversus time. For a cold rolling tandem mill, there are three conditionsfor energizing the GFLAG and Goose logic control, and thus, the impactload conntroller 28. These three conditions are shown on lines I, III,and IV of FIG. 7A, and are 1) if the speed error WE is greater thanWEMAX 2; 2) if the stand speed feedback is less than WPUMIN; and 3) ifthe stand speed reference is less than WPURMIN. The "WEMAX 2" conditionis the pickup point for operation of the impact load controller 28 asshown in the speed error curve near the bottom of FIG. 7B. The minimumvalue for actual speed at which the stand is operating during thethreading phase is represented by "WPUMIN," and the minimum value for adesired or reference speed for the stand in the threading phase isrepresented by "WPURMIN."

Preferably, for assured operation of the Goose control of the invention,the speed error WE will exceed 0.5% of the maximum stand speed, and thestand speed reference WPURMIN and the stand speed WPUMIN will both beless than 3.8% of the maximum stand speed. This maximum stand speed maybe as low as 200 ft/minute and as high as 500 ft/minute for thethreading operation of a tandem cold rolling mill.

The impact load controller 28 is de-energized when the speed error WEbecomes the drop out point for the operation of the invention or becomesless than "WEMAX 1" as shown in the speed error curve near the bottom ofFIG. 7B and indicated on line II of the logic diagram of FIG. 7A, oruntil the strip has been in the stand for two seconds as indicated online V. These lines, I, II, II, IV, and V of FIGS. 7A-7B have associatedwith them control relays CRa, CRb, CRc, CRd, and CRe.

In a cold rolling mill, relays CRa, CRb, CRc, CRd, and CRe come intoplay for activation and deactivation of the GFLAG and Goose logicsignals in the threading phase of the mill because the mill operates atlow mill speeds to activate all the relays. In a hot mill, only relaysCRA, CRb, and CRe come into play, and relays CRc and CRd are notapplicable as shown in FIG. 7B. In a hot mill, the threading speeds arerelatively high thereby preventing the speed and speed detectorsrepresented along lines III and IV from being energized.

The flowcharts for a program for the operation of the impact loadcontroller 28 of the present invention in a microprocessor type ofcontrol arrangement is shown in FIGS. 8A to 11B.

The logic diagram of FIG. 7B has on Line VI a relay entitled "ImpactLoad--Goose Controller Selected." These FIGS. 8A-11B show steps involvedfor the operation of the Goose controller of the load impact controller28. If the Goose controller is not selected, the program goes down alongline ∓A" to the bottom of FIG. 11B to blocks 62 to 72 where "FIRSTGOOSE" and GFLAG are set to "False;" COUNTG and WEG are each set tozero; and WEZ is made equal to WE; and then to block 73 where WIG is setto zero. These variables can be reset for another threading operation ofthe mill. If the Goose controller is selected, the first test is todetermine whether the strip is in the stand as indicated by SISIN inblock 74. If "no," then COUNTG which is a timer is set to zero as seenin block 76, and the program proceeds to the next test in block 78. Ifthe answer is "yes" to the test in block 74, the program proceeds to atest in block 80 asking whether COUNTG is less than COUNTGMAX which is apreset value in the microprocessor. If the answer in the test of block80 is "no," this indicates that the strip in the stand has been in theroll bite for two (2) seconds or more, and COUNTG is set to COUNTGMAX,as indicated in block 82. If the answer to the test in block 80 is"yes," the time counter is incremented by 1 as indicated in block 84.

The program proceeds from blocks 82 and 84 to the test control in block78. This test in block 78 is to see whether the Goose control turn "on"is to be checked. Three conditions are necessary in order for this testto be satisfied. These conditions are "strip not in stand" (NOT SISIN),and COUNTG is greater than zero, but less than COUNTGMAX. If the answerto test 78 is "no," the Goose control is "off," and the followingvariables are set as shown in blocks 86 to 94 where FIRST GOOSE is setto TRUE; GFLAG=FALSE; WE=0; WEZ=WE; and WIG=Low Pass Filter. This lastblock 94 indicates a subroutine where WEG is a new output, WIG is theprevious output, and Goose Filter TC is the tuning package. The outputfrom subroutine 94 goes along line "B" to the bottom of FIG. 11B whereit goes to junction 75.

If the answer to test 78 in FIG. 8B is "yes", then the Goose control ofthe impact load control 28 is "on." The program proceeds along line "C"to the test in block 96 in FIG. 9A. This test in block 96 tests to seeif the speed and the speed reference requirements are met. The twoconditions which must be met are: 1) the stand speed feedback, WPUFEEDBACK SPEED, be less than the minimum speed for the stand (WPUMIN),and 2) the final stand speed reference be less than the minimum speedreference (WPURMIN). If the answer to block 96 is "no," this interpretsthe drive motor 12 as running at a high speed value for the mill. Theprogram proceeds down along line "d" to FIG. 11A to blocks 98, 100, 110,112, and 114 where FIRST GOOSE=TRUE; GFLAG=FALSE; WEG=0; WEGZ=WE; andWIG=Low Pass Filter. Block 114 is a subroutine similar to that of block94 of FIG. 8B. From block 114, the program proceeds to junction 75.

If the answer to test 96 in FIG. 9A is "yes," then the drive speed ofmotor 12 is a low threading speed for the stand, and therefore, theGoose control can be turned "on." A further test in block 116 tests tosee if the speed error is sufficient to turn the Goose control "on." Twoconditions must be met: 1) the speed error WE has to be greater thanWEMAX 2; and 2) the "FIRST GOOSE" is not going through the impact loadcontroller 28.

If the answer to the test in block 116 is "yes", the Goose control is"on," and the program proceeds to blocks 118, 120, and 122 where GFLAGis set to "True"; WEG is set to WE; and WEG is made equal to (GAIN)[WEG-WEGZ], where [WEG-WEGZ] is the difference in the present andprevious speed errors in unit 44 of the load impact controller 28 ofFIG. 5. From block 122, the program proceeds to blocks 124, 126, and 128in FIG. 10A, where WIG=Low Pass Filter, WEGZ=WE; and FIRST GOOSE=FALSE.Block 124 is a subroutine similar to that of blocks 94 and 114.

From block 128 of FIG. 10A, the program proceeds along line J tojunction 75 at the bottom of FIG. 11B. Referring again to FIG. 9A, ifthe answer to the test in block 116 is "no" the program proceeds to testblock 130. This block 130 tests to see if the maximum speed error hasbeen exceeded. If the answer is "no" the Goose control is "off." Theprogram proceeds along line D to blocks 132 and 134 in FIG. 10B. Inblock 132, FIRST GOOSE is set to TRUE, and in block 134, GFLAG is set toFALSE. From block 134, the program proceeds along line H to blocks 135,137, and 139 of FIG. 11A, and eventually to junction 75. In these blocks135, 137 and 139 WEG=0, WEGZ=WE, and WIG=Low Pass Filter (WEG, WIG,GOOSE FILTER TC), respectively.

If the answer to the test in block 130 is "yes", then the Goose controlis "on". Test block 136 provides for a correction to the Goose control.If "yes", it is the First Window for the program, and the programproceeds to set GFLAG=TRUE in block 138. From line F, the programproceeds from block 138 to blocks 140, 142, 144 and 146 of FIG. 10A.Block 140 sets WEG to WE; and block 142 sets WIG to (GAIN) [WEG-WEGZ]2^(RATE) SHIFT which is derived from components 44 and 46 of the impactload controller 28 of FIG. 5. Block 144 sets WEGZ to WE. Block 146 setsFIRST GOOSE to FALSE. The program proceeds from block 146 to junction148, and along I to FIG. 11 to eventually come to junction 75.

Referring to again to FIG. 9B, if the test in block 136 is "no", thenthe input is through the impact load controller 28 for the first time.The program proceeds along line E to blocks 150, 152, 154, 156 and 158,where GFLAG=TRUE; WEG=WE, WEG=(GAIN) [WEG-WEGZ], WIG=Low Pass Filter;and WEGZ=WE. The block 156 is a subroutine similar to block 94. Block154 contains the difference in the previous and present speed errors.The program proceeds from block 158 to junction 148, and along line I toFIG. 11A, and eventually to junction 75.

The impact load controller 28 for a stand of a rolling mill will beautomatically operated basically during the threading phase as the stripenters the roll bite and will continue to operate for approximately twoseconds thereafter.

The impact load controller 28 will be operated preferably in parallelwith (PI)² speed controller 30, for controlling (PI) speed controller34.

FIGS. 12a and 12b show a typical speed regulator response when (PI)²speed controller 30 is operated without the impact load controller 28 ofthe invention and in series with (PI) speed controller 34. FIGS. 12c and12d show a typical speed regulator response when (PI)² speed controller30 is used in parallel with the impact load controller 28 and inn serieswith (PI) speed controller 34. The horizontal axis of FIGS. 12b and 12drepresents the steady state load current with the area above this axisrepresenting the overshoot. For the speed error curves, the bottomportion of the curves of FIGS. 12a and 12c represents the gathering ofthe strip between stands, is the integral of the rate of change in speederror with respect to time, and has a positive speed error value. Thetop portion of the curve of FIG. 12(a) represents the elimination of thestrip storage, is the integral of the rate of change in speed error, andhas a negative speed error value.

It is readily observed when comparing these FIGS. 12a and 12c that boththe maximum speed drop (speed error) and therefore the integral of thespeed error are greatly reduced when the impact load controller 28 isused in parallel with (PI)² speed controller 30. Also, it can be seenthat the current for the drive motor is greatly increased in a shorterresponse time when the impact load controller 28 is used in parallelwith (PI)² speed controller 30.

FIGS. 13a and 13b show a typical speed regulator response when (PI)speed controller 34 is operated without impact load controller 28 of theinvention and without (PI)² speed controller 30, and FIGS. 13c and 13dshow a typical speed regulator response when (PI) speed controller 34 isused in series with the impact load controller 28 and without (PI)²speed controller 30. The horizontal axis of FIGS. 13b and 13d representsthe steady state load current with the area above this line representingthe over shoot. The bottom portion of the speed error curves of FIGS.13a and 13c represents the gathering of the strip between stands, andthe top portion represents the decreasing of the strip storage similarto what was explained for FIGS. 12(a) and 12(c). When comparing FIGS.12c and 12d to FIGS. 13c and 13d it can be seen that there are betterresponse results when (PI)² speed controller 30 is used in parallel withimpact load controller 28 and in a series with (PI) speed controller 34,as opposed to the impact load controller 28 only being used in serieswith (PI) speed controller 34 without the use of (PI)² speed controller30. Also, it can be seen that better response results are obtained whenusing the impact load controller 28 as opposed to not using controller28.

FIGS. 14a, 14b, and 14c again represent a typical speed regulatorresponse when (PI)² speed controller 30 is used in parallel with impactload controller 28 and in series with (PI) speed controller 34. FIGS.14a and 14c are similar to FIGS. 12c and 12d. FIG. 14b represents theoutput signal of impact load controller 28 when the strip is in thestand for a two second time interval. The curve shows a vertical line or"spike" followed by a smooth gradual decaying exponential portion. Theuse of components 44 and 46 as taught hereinbefore produces an initialsharp increase in the dynamics of the system and filter 50 allows agradual, slow decay in the response of the system.

Impact load controller 28 is energized when the speed error exceeds a"WEMAX 2" setting. This is represented in FIG. 14a by the tangent lineor slope of the curve indicated at "T". As seen inn FIG. 14b the outputsignal of impact load controller 28 jumps to a value which is a functionof the rate of change in the speed error and proportional thereto, andthen decays exponentially in a matter as a function of the time constantof the low pass filter 50 of FIG. 5. For a microprocessor control ofFIGS. 8-11, the response time is instantaneously, whereas for an analogcontrol of FIGS. 15 and 16, there may be a short time delay for theresponse.

As stated hereinbefore, the initial output of impact load controller 28is a function of the rate of change in the speed error which is based onthe actual speed and a desired speed. The rate of change in speed errorat the time of the initial impact load is a direct function of themagnitude of the impact load torque disturbance applied to the drivemotor 12 of FIG. 1. In view of this, the larger the impact load torquedisturbance, the higher the output signal of impact load controller 28.After the initial output, the output of impact load controller 28 is afunction of the low pass filter time constant setting whereby the rateof change in speed error decays exponentially as seen in FIG. 14b.

Impact load controller 28 adapts to the change in the magnitude of theimpact load torque disturbance applied to the drive motor 12, i.e. thebigger the load, the greater the output signal of the impact loadcontroller. This feature provides optimum reduction in drive speed errorfor the varying magnitudes of the load disturbances. Referring again toFIG. 1, at the onset of operation of impact load controller 28, theoutput signal passes instantly through the proportional part of (PI)speed controller 34, thus instantly providing an increase in thearmature current reference signal Ia* to armature current controller 16for control of the current to drive motor 12.

The impact load controller 28 can be either of a microprocessor type ofarrangement as described herein, or it can be of an analog typeconsisting of several electrical and logic components as shown in FIGS.15A, 15B, and 16 and having the same numerals as that shown in FIGS.1-6, and which can easily be understood by those skilled in the art.

Whereas a particular embodiment of the invention has been describedabove for purposes of the invention has been described above forpurposes of illustration, it will be evident to those skilled in the artthat numerous variations of the details may be made without departingfrom the invention as defined by the appended claims.

I claim:
 1. A speed regulator drive system for regulating the speed of a drive motor, comprising:means for determining a speed error based on an actual speed value and a desired speed value and for using said speed error during the normal operation of said drive motor, and impact load controller means for producing a first output, said first output used to compensate for a reduction in said speed from a steady state speed in said normal operation of said drive motor and for supplementing at least said speed error for said regulating of said drive motor when a load disturbance is applied to said drive motor, said impact load controller means comprising: rate controller means for receiving said speed error, for determining rates of change in said speed error, and for producing a gain value product including said rates of change in said speed error, means for initially increasing said gain value product to a first value by a desired amount to proportionately increase said speed of said drive motor to a value above said steady state speed, and filter means for receiving said first gain value product for precharging said filter means and for subsequently receiving second gain value products for exponentially decreasing said speed of said drive motor until said speed reaches said steady state speed.
 2. A drive system of claim 1, further comprising:(PI) speed controller means used in series with said impact load controller means for said regulating of said speed of said drive motor.
 3. A system of claim 2, further comprising:(PI)² speed controller means used in parallel with said impact load controller means for receiving said speed error to generate a second output, and means for combining said speed error with said first output of said impact load controller means and with said second output from said (PI)² controller means to generate a signal for controlling said (PI) speed controller means for said regulating of said speed of said drive motor.
 4. A system of claim 1, wherein said rate controller means comprises:means for storing and updating said speed error, means for calculating the difference between an updated speed error and a stored speed error, and means for multiplying said difference between said updated speed error and said stored speed error to product said gain value product.
 5. A system of claim 1, wherein said rate controller means operates on the following transfer function: ##EQU7## where S is a Laplace operator in 1/seconds, T_(d) is an updated time unit in milliseconds for said speed regulator drive system, and Z⁻¹ =_(e) -T_(d) S, and K_(g) is a constant.
 6. A system of claim 1, wherein said rate controller means further comprises rate transfer function means having a Laplace operator.
 7. A system of claim 1, wherein said filter means is a low pass filter of first order operating on the following transfer function: ##EQU8## where TC is a time constant setting for said filter means, and S is a Laplace transformer in 1/seconds.
 8. A system of claim 1, wherein said means for initially increasing said gain value product includes the number 2 raised to a desired integer value.
 9. A system of claim 1, wherein said rate controller means and said filter means each comprises adjustment means.
 10. A system of claim 1, wherein said impact load controller means further comprises microprocessor means for activation and deactivation operation of said impact load controller means.
 11. A system of claim 1, wherein said impact load controller means further comprises microprocessor means for operation of said impact load controller means.
 12. A system of claim 1, wherein said system is a multiloop system comprising an inner loop current control and an outer loop speed control, andwherein said impact load controller means is part of said outer loop speed control and operates in series with proportional integrator means and in parallel with proportional integrator squared means.
 13. A system of claim 12, wherein said system is part of a main system for a rolling mill and controls the speed of two work rolls of a stand of said mill, which work rolls receive material to be rolled, andwherein said main system includes means for detecting the entry of said material between said work rolls during the threading phase of said mill and means for activating and deactivating the operation of said impact load controller means within a desired time integral after said entry of said material.
 14. A system of claim 13, wherein said rolling mill is a cold tandem mill, and said impact load controller means includes a logic system having a predetermined set of conditions for operation thereof in said cold tandem mill.
 15. A system of claim 13, wherein said rolling mill is a hot tandem mill and said impact load controller means includes a logic system having a predetermined set of conditions for operation thereof in said hot tandem mill.
 16. A speed regulator drive system for regulating the speed of a drive motor and having first speed controller means, comprising:means for determining a speed error which is the difference between an actual speed value and a desired speed value, and impact load controller means for compensating for a reduction in said speed from a steady state condition due to a load disturbance applied to said drive motor, said impact load controller means comprising: filter means, and means for producing an initial signal and a series of sequential signals which are a function of a rate of change in said speed error, and including means for applying said initial signal to said first speed controller means for an increase in said speed of said drive motor which is greater than said steady state condition, and for applying said sequential signals to said filter means for further control of said first speed controller means for exponentially decaying said speed of said motor to its said steady state condition.
 17. A system of claim 16, wherein said means for producing said initial signal and said sequential signals further comprises:a first multiplier means for obtaining a gain value for said initial signal and said sequential signals.
 18. A system of claim 17 wherein said means for producing said initial signal and said sequential signals further comprises:second multiplier means, and means for applying a signal of said second multiplier means to said initial signal.
 19. A system of claim 16, wherein said filter means is a low pass filter of the first order.
 20. A system of claim 19, wherein said filter means includes means for operating on the following transfer function: ##EQU9## where TC is a time constant for said filter means, and S is a Laplace transformer in 1/seconds.
 21. A system of claim 16, wherein said system further comprises second speed controller means and means for operating said second speed controller means in parallel with said impact load controller means.
 22. A system of claim 16, wherein said system further comprises means for operating said first speed controller means in series with said impact load controller means.
 23. A system of claim 21, wherein said first speed controller means has (PI) characteristics, and wherein said second speed controller means has (PI)² characteristics.
 24. A system of claim 16, wherein said means for producing said initial signal and said sequential signals includes means for operating on the following transfer function: ##EQU10## where S is a Laplace operator in 1/seconds, T_(d) is an updated time unit in milliseconds for said speed regulator drive system, and Z⁻¹ =e^(-T) d^(S) and K_(g) is a constant.
 25. An impact load controller for controlling the dynamics of a drive motor whose speed is reduced from a steady state condition due to a load disturbance applied to said motor, said impact load controller comprising:means for producing a signal which is a function in a rate of change in a speed error, which speed error is the difference between a desired speed value and an actual speed value, and including means for producing a gain value product for said signal, and means for applying said signal to said drive motor to first increase said speed of said drive motor above said steady state condition and to sequentially decrease said speed of said drive motor until it reaches said steady state condition.
 26. A method for controlling the dynamics of a drive motor whose speed is reduced from a steady state speed due to a load disturbance applied to said motor, the steps comprising:using a rate of change in speed error, which speed error is based on the difference between a desired speed value and an actual speed value, producing a gain value product for said rate of change in said speed error, combining said gain value product with at least said speed error to initially increase said speed of said drive motor above said steady state speed, and thereafter to decrease said speed of said drive motor until it reaches said steady state speed.
 27. A method for compensating for a reduction in speed of a drive motor from a steady state speed due to a load disturbance applied to said drive motor, the steps comprising:(a) determining a speed error based on an actual speed value and a desired speed value, (b) determining the rate of change in said speed error, (c) producing a gain value product for said rate of change in said speed error, (d) initially increasing said gain value product to a first value by a desired factor to proportionally increase said speed of said drive motor above said steady state speed, and (e) after said initial increase in said speed of said motor, filtering sequentially said gain value products to exponentially decrease said speed of said drive motor until said speed reaches said steady state speed.
 28. The method of claim 27, the steps further comprising:using a (PI) speed controller to receive said first gain value product and said sequential gain value products for regulating the speed of said drive motor.
 29. The method of claim 27, the steps further comprising:using a (PI)² speed controller for receiving said speed error and for producing an output, and combining said output from said (PI)² speed controller with at least said sequential gain value products to produce a combined output which is used to regulate the speed of said drive motor.
 30. The method of claim 29, the steps further comprising:using a (PI) speed controller to receive said combined output for said regulating of said speed of said drive motor.
 31. The method of claim 27, the steps further comprising:using a low pass filter of the first order for said filtering step, and operating said filter on the following transfer function: ##EQU11## where TC is a time constant for said filter and S is a Laplace transfer in 1/seconds.
 32. The method of claim 31, the steps further comprising:using tuning means for changing said time constant for said filter in a range from zero to 200 milliseconds.
 33. The method of claim 27, the steps further comprising:for steps (b) and (c) using the following transfer function: ##EQU12## where S is a Laplace operator in 1/seconds, T_(d) is an updated time unit in milliseconds, and Z⁻¹ =_(e) -T_(d) S, and K_(g) is a constant.
 34. The method of claim 33, the steps further comprising:using tuning means for changing said gain value product for said rate of change in said speed error in a range from zero to fifteen milliseconds.
 35. A method of claim 27, the steps further comprising:for step (d), using the integer two raised to a power ranging from zero to five for said desired factor.
 36. In a speed regulator drive system in which the speed of a drive motor is controlled by a speed error signal, a load impact controller for compensating for reduction in speed of said drive motor from a steady state speed due to impact loads, said load impact controller comprising:means for generating a load impact correction signal which is a step function of the rate of change of the speed error and modified to decay with time, and including means for generating a rate signal proportional to said rate of change of said speed error, and summer means for adding said load impact correction signal to said speed error signal to control the speed of said drive motor for returning said drive motor to its said steady state speed.
 37. The system of claim 36, wherein said means for generating said load impact correction signal further includes:means for multiplying said rate signal by a gain factor, low pass filter means, and means for initially selecting said rate signal multiplied by said gain factor as the load impact correction signal, and subsequently selecting said rate signal filtered by said low pass filter means as said load impact correction signal.
 38. The system of claim 37, wherein said means for generating said load impact correction signal further includes means for applying said rate signal multiplied by said gain factor to said low pass filter means as an initial charge.
 39. The system of claim 38, further including means for operating said means for generating said load impact correction signal only when said speed error signal rises above a first predetermined threshold.
 40. The system of claim 39, wherein said means for generating said load impact correction signal drops out when said speed error signal falls below a second predetermined threshold below said first threshold.
 41. The system of claim 37, including a (PI)² controller generating a (PI)² error signal as a function of said speed error signal, andwherein said summer means includes means for adding said (PI)² error signal to said speed error signal and said load impact correction signal to control said speed of said drive motor. 